Clinical practice guidelines (CPGs) are intended to enhance the practice of evidence-based medicine by streamlining healthcare delivery and improving the process and outcomes of patient care. Recently, concerns have been raised about the potential for bias when treatment recommendations are developed by industry-funded researchers. Bias in CPGs creates the potential to expose patients to harm from unnecessary treatment or from treatment that is not evidence-based. Concerns that the trustworthiness and clinical utility of CPGs were being compromised because of financial conflicts of interest (FCOI) on the part of guideline authors led the Institute of Medicine (IOM) to recommend that guideline developers avoid FCOI. The IOM explicitly states that the guideline chair should not have FCOI. However, to date, no study has simultaneously examined the FCOI of guideline development groups (GDGs) and assessed its influence on the quality of guidelines. The purpose of the proposed project is to determine whether an association exists between GDGs' financial ties to industry and guideline quality in a subset of guidelines for Major Depressive Disorder (MDD). CPGs for MDD were chosen for this project because of the social, economic, and public health burden of depression. An additional outcome of this study will be the development of a novel quality assessment tool that is reliable, valid and robust enough to detect negative effects that FCOI may have on guideline quality. This tool will have clinical utility for the quality assessment of CPGs for all medical specialties. A systematic review will be conducted to identify CPGs for depression. Each guideline will then be assessed for threats to internal and external validity using the quality assessment tool being developed as part of this project. Our methodology will allow us to assess whether FCOI (defined as financial ties to manufacturers of antidepressants) in GDGs result in guidelines with fewer markers of high quality. We will also examine the relationship between GDGs' industry ties and recommendations favorable to industry, defined as recommending the use of antidepressants as a first line treatment for mild and moderate depression. The results of this study will provide information about the quality of CPGs for MDD and thus will be relevant to patients, mental health practitioners, and public and private policy makers. The results will also aid in improving guideline development by providing data that can inform decisions about when to disclose or manage FCOI and when to prohibit industry relationships within GDGs. This study's research design, new methodology, and new data (the relationship between FCOI and guideline quality in a subset of CPGs) may have a substantial impact on future studies assessing the quality of CPGs for other disease categories.